Direct-controlled valves of the above type are generally known in the art as a specific form of hydraulic switching elements belonging to the group of proportional distributing valves. Due to their compact structure and inexpensive manufacture, and also because of their simple exchangeability and excellent switching properties, such cartridge valves are also being increasingly used in internal combustion engines equipped with a device for varying valve timing. Within the hydraulic system of these devices, the cartridge valves control the flow of engine oil from the oil supply point to the adjusting device and back into the crankcase of the internal combustion engine. The cartridge valves are generally arranged in an insertion bore having approximately the same diameter as the annular webs of the cartridge valve in the cylinder head of the internal combustion engine. The pressure medium supply ducts open radially into this insertion bore which one attempts to make by the simplest possible manufacturing procedure so that it forms, together with the annular webs of the cartridge, an annular gap seal between the individual annular chambers in the insertion bore.
Notwithstanding a precise fabrication of the insertion bore and the cartridge, it has been determined that the radial clearance between the radial webs of the cartridge and the bore wall of the insertion bore is occasionally so large that leaks or hydraulic short circuits occur between the annular chambers in the insertion bore so that an adequate hydraulic support of the adjusting piston of the adjusting device is no longer guaranteed. The influence of the radial clearance on leakage can certainly be compensated for by the choice of an appropriate length of the annular gap (wider annular webs) but this requires a certain additional amount of axial design space which is often not available.
To avoid leakages resulting from the radial clearance, two narrower, spaced annular webs were provided in place of each annular web on the cartridge valve and an O-ring seal was arranged in the space between the annular webs. When such cartridge valves are inserted into the insertion bore, the O-ring seals which extend radially beyond the annular webs can be sheared off in the region of the radial pressure medium supply ducts in the insertion bore due to the sharp edges of the duct openings so that, in this case too, tightness between the annular chambers is not guaranteed. To avoid this problem, the radial pressure medium supply ducts in the insertion bore are made as stepped bores, or comprise a countersink at the transition to the insertion bore. In both cases, the transition from the insertion bore to the radial pressure medium supply ducts is tapered so that the danger of shearing of the O-ring seals during the insertion of the cartridge valve into the insertion bore is reduced. The fabrication of an insertion bore with pressure medium supply ducts of the aforesaid type is, however, rather complicated and consequently expensive.
As an alternative solution for avoiding the high costs involved in the making of these stepped bores, DE-OS 44 34 142 proposes a method for the mounting of a first element in a second element. Before insertion of the first element into the second element, the sealing members together with the first element are deformed in a receptacle of a cooling device to the extent to which they would also be deformed in their installed state. The sealing elements are cooled in this deformed state so far that their state of elastic deformation is maintained for some time. Since the sealing elements now no longer protrude beyond the first element, said first element together with the sealing elements can now be installed with ease in the second element. After assembly, the sealing elements return to normal temperature and reacquire their elastic properties. However, this method requires separate cooling devices which, due to their manufacturing, maintenance and energy costs and also because of the prolongation of assembly time by the cooling operation, have a negative effect on the total mounting costs.